Understanding the environmental impacts of large-scale cellulose nanocrystals production: Case studies in regions dependent on renewable and fossil fuel energy sources

Favorable functional properties of cellulose nanocrystals (CNCs) in several end-use applications as well as its 'green' credential as a bio-based material, stimulate significant interest in scaling up the manufacture of CNCs. As in any other process, there exist several design options for the overall process and decisions on adoption of a specific plant configuration should be based on the economic as well as the environmental data, preferably from the life cycle assessment (LCA) perspective. In this study we establish a benchmark LCA of a conceptual large-scale CNC manufacturing process based on sulfuric acid hydrolysis. We then employ the benchmark process model to explore several plant configurations under different acid recycling scenarios and targeting two different CNC materials, revealing key findings: (1) without acid recycling environmental impacts are dominated by input materials; (2) introducing acid recycling shifts environmental impacts from input materials to energy consumption: thus, complete acid recycling requires similar to 14 times more energy; (3) based on the LCA study we recommend optimizing plant configuration through partial acid recycling for a balance between materials and energy consumption. Regions with abundant low-carbon energy, like Quebec and Sweden, favour high acid recycling, while fossil-dominated regions benefit from limited acid recycling. This study provides benchmark values of LCA impacts of CNC manufacture, which could be used for the assessment of carbon footprint and other environmental metrics of final products manufactured from CNCs.